Horological disquisitions concerning the nature of time, and the reasons why all days, from noon to noon, are not alike twenty four hours long in which appears the impossibility of a clock's being always kept exactly true to the sun : with tables of equation, and newer and better rules ... how thereby precisely to adjust royal pendulums ... : with a table of pendulums, shewing the beats that any length makes in an hour ... / by John Smith ... ; to which is added The best rules for the ordering and use both of the quick-silver and spirit weather-glasses, and Mr. S. Watson's rules for adjusting a clock by the fixed stars.

The Way of finding how much a Pendulum Clock has gained or lost in a Day, Week or a Month, to the nicity of Two or Three Seconds, &c.

N.	h.	′	″
1	0	3	56
2	0	7	52
3	0	11	48
4	0	15	44
5	0	19	39
6	0	23	35
7	0	27	31
8	0	31	27
9	0	35	23
10	0	39	19
11	0	43	15
12	0	47	11
13	0	51	7
14	0	55	2
15	0	58	58
16	1	2	54
17	1	6	50
18	1	10	46
19	1	14	42
20	1	18	38
21	1	22	34
22	1	26	30
23	1	30	25
24	1	34	21
25	1	38	17
26	1	42	13
27	1	46	9
28	1	50	5
29	1	54	1
30	1	57	57
31	2	1	53

TAke a Piece of thin Brass, and file there∣in a Slit or Notch, about half a quar∣ter of an Inch deep, but somewhat wider at the Top than at the Bottom, as thus 〈◊〉〈◊〉, knock the End of it into some Post in your Back-side, or else in some Window, that ye think convenient; then look through the Notch at any Star of the first or second Mag∣nitude, and wait till the Star comes to the Edge of any Chimney, or the Side of any House, and you will see the Star vanish in a Moment; then mark what your Clock is at

when the Star vanishes: Then at any other Night afterwards (as the next Night, or a Week or a Month afterwards) wait for the same Star again till it vanish behind the Chim∣ney or House, as before, and then observe what your Clock is at, then your Clock should shew the second Time of vanishing so much sooner than the first, as this Table shews; now the farther off the Chimney or Wall is the more exact will the Observation be. Let the Distance be Ten Yards at least, let the Observation be made in any part of the East, South or West, but little towards the North Pole, because the Polar Stars are not so fit for this Purpose.

EXAMPLE.

Suppose a Star vanishes this Night at Nine Hours, Three Minutes and Four Seconds, by my Clock, and Eight Nights after I observe it again, and it then vanishes at Eight Hours, Thirty four Minutes and Forty two Seconds; by my Clock, against Eight Nights, in the Table, I find Thirty one Minutes Twenty se∣ven Seconds; that is, so much sooner should the Star vanish at the second Observation than it did at the first; therefore substracting 31′ 27″ from the first Observation 9h. 3′ 4″. there's left 8h. 31′ 37″, the true Time that the Clock should have been at in the second Observation; therefore seeing the Clock was then at 8h 24′ 32″, it has gained 2′ 55.